The present invention relates to a dual port memory device, and more particularly to a serial data input device for use in a dual port memory device.
Contemporary image display devices operate at increasingly higher speeds and with greater image resolution. Thus, memory devices used to store image data must operate at high speeds. It is also desirable for such memory devices to be highly integrated. Conventional dual port memory devices have been used to store image data for image display devices. When so configured, a conventional dual port memory device typically includes a random port adapted to randomly access data, and a serial port adapted to serially access data.
FIG. 1 shows an input/output (I/O) section for a serial port in a conventional dual port memory device. As shown in FIG. 1 the serial port I/O section includes a memory cell array 10 which is typically a RAM, a data register 12 used to interchange data with memory cell array 10, a selector 14 which selects between operating modes for data register 12, a serial counter 16 which controls selector 14 in accordance with an external control signal, a serial write driver 20 which supplies a serial data input to data register 12, a serial I/O and sense amplifier 18 for transferring data from data register 12 to an external memory device, an I/O buffer 22 for receiving/transferring and converting incoming and outgoing data, and a date transfer controller 24 for controlling data transfer operations between memory cell array 10 and data register 12.
In operation, the I/O section of the conventional dual port memory device receives incoming data via an input pad from an external memory device at I/O buffer 22. I/O buffer 22 converts the incoming data signals to CMOS compatible signal levels, and transfers the data to data register 12 via serial write driver 20. Thus, a serial write operation generally consists of two steps. First, data is received (or input) at I/O buffer 22, or an analogous component. Second, the received data is transferred from I/O buffer 22 to data register 12 in order to be stored in memory cell array 10. The time delay between these first and second steps necessarily limits the speed at which serial write operations can be performed in conventional dual port memory devices. In fact, serial write operations through a single input port in conventional dual port memory devices are generally too slow to service contemporary image display devices.
In order to overcome this shortcoming, conventional dual port memory devices have resorted to the use of multiple serial data input ports. Until now, the use of multiple serial input ports was the only way to dump serial data to such memory devices at high speed. Unfortunately, limitations on available integrated circuit pin outs (or pads) make the allocation of multiple ports to serial data operations impracticable, if not impossible.